Source dilution sampling system for emissions analysis

ABSTRACT

A system for sampling emission products from an emissions source, for example combustion engines including gasoline, diesel and natural gas engines, for subsequent measurement and analysis of the emission products. The system includes a dilution apparatus, a residence time chamber, a plurality of sampling probes within the residence time chamber, and a plurality of sampling trains connected to the sampling probes to take simultaneous representative emission samples for subsequent analysis. The system has particular use in quantifying chemical and toxic trace species from emissions sources. The results of the analysis can be used to formulate decisions on changes in engine design strategy, and can be used to determine the effectiveness of aftertreatment systems on the emissions source.

PRIORITY INFORMATION

This application is a Divisional Application of U.S. application Ser.No. 11/530,728 filed Sep. 11, 2006 entitled SOURCE DILUTION SAMPLINGSYSTEM FOR EMISSIONS ANALYSIS, which is hereby incorporated by referencein its entirety.

FIELD

A system for sampling emission products from an emissions source, forexample combustion engines including gasoline engines, diesel engines,and natural gas engines for subsequent measurement and analysis of theemission products.

BACKGROUND

Emissions of pollutant chemicals have increased orders of magnitudes inthe past 100 years due primarily to anthropogenic releases associatedwith industrial, agricultural, domestic, and recreational activity.Current research indicates that there are very strong correlationsbetween the increase in these emissions and an overall increase inatmospheric temperatures (i.e. global warming) and an increased numberof Category 4 and 5 hurricanes per annum. Furthermore, it is believedthat ambient particulate matter in aerosol phase may include potentiallytoxic components. Researchers also believe that particulate matter andgases from industrial activities and vehicles may cause various healthproblems, such as asthma. These correlations between emissions ofpollutant chemicals and the negative impact on environment and humanhealth has led to more stringent worldwide emission standards forautomobiles and other vehicles, as well as power plants, mines, andother industries.

In the United States, emission standards are set by the EnvironmentalProtection Agency (EPA) as well as state governments (e.g. CaliforniaAir Resource Board (CARB)). As of this writing, all new vehicles sold inthe United States must meet the EPA's “Tier 1” emission standard. A morestringent standard, “Tier 2,” is being phased in for automobiles andshould be completed by 2009. For diesel engines, on-road trucks andother vehicles will be required to meet more stringent standards by 2010and off-road vehicles such as construction vehicles will be subject toTier IV regulations. Accordingly, attaining ultra low emissions hasbecome a top priority for combustion researchers as federal and stateregulations continuously reduce the allowable levels of pollutants thatcan be discharged by engines, power plants, and other industrialprocesses.

In order to meet the emission standards of today and the future,researchers have made, and are continually striving to make,improvements to combustion engines, for example heavy duty dieselengines, gas combustion engines, power-generating gas turbines, and thelike, and other emission sources. In addition to these developments,researchers are endeavoring for better methods and devices of measuringsmaller particulate matter and low level gases and quantifying thechemical compositions of emissions.

Generally, chemical composition analysis of fine particulate matter,gases, and volatile and semi-volatile organic compounds from emissionssources consists of three major steps: (1) Representative conditioningand sampling; (2) Chemical analysis; and (3) Data analysis andexplanation. The effective accuracies of Steps (2) and (3) are bothdependent on step (1). For without an accurate and precise samplingprocedure, no analysis of that sample could be said to represent validdata. Accordingly, without valid analysis, a full and completeexplanation of the sample would not be available.

A conventional system for assessing particle mass and quantifyingchemical composition of emission gases mixes emission gas with filteredair in a mixing chamber. The conventional system is illustrated in FIG.1, and includes a sampling port 2 that feeds exhaust gases to a diluter4, forming the mixing chamber, where the exhaust gases are diluted withthe filtered air. The diluted gas mixture is then sampled by a samplingtrain 6. However, this system has many well recognized disadvantages.First, the partial/full/partial dilution sampling system in thisconventional system would introduce more errors than a full/partial/fullsystem. Second, the conventional system allows only for assessment ofsingle type of compound. Accordingly, multiple sample runs are requiredto detect each of the chemical compounds necessary for a full compoundassessment (particulate matter, volatile organics, semi-volatileorganics, and gases, etc.) Furthermore, these measurements are made withdifferent samples each time, and may add to inherent errors that areunavoidable to this system. These errors may lead to inaccuratemeasurements and quantification of data.

Work at the University of Wisconsin-Madison attempted to improve theconventional system. University of Wisconsin scientists used a devicecalled an “augmented sampling system” to study the chemical compositionand to assess particle size of diesel engine exhaust. See Chol-BumKweon, David E. Foster, James J. Schauer, and Shusuke Okada, “DetailedChemical Composition and Particle Size Assessment of Diesel EngineExhaust” SAE 2002-01-2670, Fall SAE Meeting 2002. The “augmentedsampling system” disclosed by Kweon et al includes a secondary dilutiontunnel for the diesel exhaust and a residence time chamber with radialsampling ports near the base of the residence time chamber. Thesecondary dilution tunnel of the augmented sampling system mixesfiltered air with an emission gas sample without regard to temperaturegradient between the surface of the dilution tunnel and the emissiongas. This may lead to a high degree of particle loss and accordinglyless accurate sampling due to thermophoresis.

Thermophoresis, or Ludwig-Soret effect, is thought to be related toBrownian movement biased by a temperature gradient. The thermophoreticforce is a force that arises from asymmetrical interactions of aparticle with the surrounding gas molecules due to a temperaturegradient. Generally, a particle is repelled from a hotter surface andattracted to a cooler surface. Thus, as emission particles travelthrough a sampling system, cooler surface temperature of the system ascompared to the emission gas would lead to greater thermophoretic forceon the emission particles.

In the Kweon et al. augmented sampling system, the residence timechamber is heated to reduce thermophoresis. However, the heatedresidence time chamber is likely to fail in achieving realisticatmospheric conditions, as the addition of heat may underestimate theparticulate matter emissions due to the reduced effects of nucleationand condensation and may also affect secondary reactions of volatileorganic compounds and semi-volatile organic compounds and formation ofsecondary organic compounds.

A system that allows more accurate and precise sampling of emissionproducts is needed, thereby contributing to better measurement andanalysis of the emission products.

SUMMARY

A system is provided for sampling emission products from an emissionssource, for example combustion engines including gasoline, diesel andnatural gas engines, for subsequent measurement and analysis of theemission products. The system has particular use in quantifying particlesize distributions and chemical species from low emissions sources. Theresults of the analysis can be used to formulate decisions on changes inengine design strategy, and can be used to determine the effectivenessof aftertreatment systems on the emissions source.

The system uses a full/partial/full approach and includes an isokineticsampling nozzle, a dilution apparatus, a residence time chamber, aplurality of sampling probes within the residence time chamber, and aplurality of sampling trains connected to the sampling probes to takesimultaneous representative emission samples for subsequent analysis.

The dilution apparatus is designed to be thermophoretic-resistant toreduce the thermophoretic force on emission particles, thereby reducingparticulate matter losses. In addition, the dilution apparatus isdesigned to simulate atmospheric dilution, mixing and cooling processes,enabling the sampled gas and the dilution gas to thoroughly mix and coolto ambient temperature, allowing gas-phase organics in the sampled gasto nucleate and condense to their usual aerosol phase.

The residence time chamber is designed to provide sufficient time forgas-to-particle conversion, which involves the diffusion limitedtransport of supersaturated vapor onto existing particles. Preferably,the residence time chamber is designed to provide at least 30 seconds ofresidence time. During this time, the sample flow and concentrationswithin the residence time chamber also become uniformly distributedbefore entering the sampling probes.

The sampling probes are aligned coaxial to the flow direction within theresidence time chamber (i.e. isoaxial) with the inlets of the probesfacing into the direction of flow. This improves collection of theemission samples since the samples do not need to turn sharp corners toenter the probes. The plurality of sampling trains connected to thesampling probes permit the simultaneous sampling of different materials,including, but not limited to, volatile and semi-volatile organic,gas-phase, and particulate matter samples.

A method of sampling emission products from an emissions source is alsoprovided. The method includes directing a sample of a gas stream fromthe emissions source into a dilution apparatus. In the dilutionapparatus, heat is exchanged between the gas stream sample and adilution gas to cool the gas stream sample, and thereafter the dilutiongas is introduced into the gas stream sample to mix with the gas streamsample. The gas mixture is then directed to a residence time chamber,and a sample of the gas mixture is taken from the residence time chamberthrough a sampling probe having an inlet that is substantially parallelto a direction of flow of the gas mixture within the residence timechamber.

In one embodiment, a system for sampling emission products from anemissions source comprises a dilution apparatus connected to a samplingprobe to receive a gas stream sample. The dilution apparatus includes aninlet through which the gas stream sample enters, a dilution gas inletthrough which dilution gas enters the dilution apparatus, and an exitthrough which a mixture of dilution gas and the gas stream sample exitsthe dilution apparatus. A dilution gas source is connected to thedilution gas inlet of the dilution apparatus for supplying dilution gas.A residence time chamber is connected to the dilution apparatus andreceives therefrom the gas mixture. The residence time chamber includesa plurality of isoaxial sampling probes disposed inside the chamber.Further, a sampling train is connected to each of the isoaxial samplingprobes.

In another embodiment, a system for sampling emission products from anemissions source comprises a dilution apparatus connected to a samplingprobe to receive a gas stream sample. The dilution apparatus includes aninlet through which the gas stream sample enters, a dilution gas inletthrough which dilution gas enters the dilution apparatus, an exitthrough which a mixture of dilution gas and the gas stream sample exitsthe dilution apparatus, and a plurality of holes axially spaced from thedilution gas inlet which allow introduction of the dilution gas into thegas stream sample. In addition, the dilution apparatus is configured sothat the dilution gas exchanges heat with the gas stream sample prior tobeing mixed with the gas stream sample. A dilution gas source connectedto the dilution gas inlet of the dilution apparatus, and a residencetime chamber that is connected to the dilution apparatus receivestherefrom the gas mixture. Further, a plurality of sampling trains areconnected to the residence time chamber.

In yet another embodiment, a system for sampling emission products froman emissions source comprises a dilution apparatus connected to asampling probe to receive a gas stream sample. The dilution apparatusincludes a longitudinal axis, an inlet through which the gas streamsample enters, a dilution gas inlet through which dilution gas entersthe dilution apparatus, and an exit through which a mixture of dilutiongas and the gas stream sample exits the dilution apparatus. A dilutiongas source is connected to the dilution gas inlet of the dilutionapparatus, and a residence time chamber is connected to the dilutionapparatus and receives therefrom the gas mixture. The residence timechamber includes a longitudinal axis that is substantially perpendicularto the longitudinal axis of the dilution apparatus. Further, a pluralityof sampling trains are connected to the residence time chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a sampling system according to the inventionconnected to a dilution tunnel for sampling emissions from an engine.

FIG. 2 illustrates the sampling system separate from the dilutiontunnel.

FIG. 3 is a cross-sectional view of the dilution apparatus taken alongthe longitudinal axis thereof.

FIG. 4 is a detailed view of the perforations in the inner tube.

FIG. 5 is a cross-sectional view of the residence time chamber takenalong line 5-5 in FIG. 2.

FIG. 6 is a cross-sectional view taken along line 6-6 in FIG. 5.

FIG. 7 illustrates exemplary flow trains connected to the residence timechamber.

FIG. 8 illustrates additional exemplary flow trains connected to theresidence time chamber.

FIG. 9 is a flow chart of an exemplary sampling method of the invention.

DETAILED DESCRIPTION

With reference to FIG. 1, a system 10 for sampling emission productsfrom an emissions source 12 is illustrated. The system 10 is constructedto simultaneously sample a number of different emissions productsemitted from the emissions source 12. The samples can then be analyzedto permit chemical characterization of the emissions products withrespect to air toxics.

The system 10 will be described herein as being applied to the samplingand chemical characterization of diesel emission exhaust from anemissions source 12 in the form of a diesel engine. However, theconcepts described herein can be used to great advantage in sampling anumber of other types of gases from a number of other types of emissionssources, both stationary and mobile. Examples of other types of gasesincludes, but is not limited to, gas combustion engine exhaust, turbineengine exhaust, and atmospheric gas. Examples of other types ofemissions sources includes, but is not limited to, gas combustionengines, turbine engines, power plants, manufacturing plants, exhauststacks, etc.

As shown in FIG. 1, the entire exhaust from the engine 12 is ducted to adilution tunnel 16 through suitable piping 18. Filtered dilution air 20is introduced into the tunnel upstream of the discharge for the engineexhaust, with the dilution air 20 then mixing with the engine exhaust inthe tunnel 16 to dilute and cool the exhaust gas.

System

With reference to FIGS. 1-2, the system 10 includes a dilution apparatus22, a residence time chamber 24, a plurality of sampling probes 26 a, b,. . . n (FIGS. 7 and 8) within the residence time chamber, and aplurality of sampling trains 28 a, b, . . . n (FIGS. 9 and 10) connectedto the sampling probes to take simultaneous representative emissionsamples for subsequent analysis.

The dilution apparatus 22 is connected to a sampling probe 30 thatextends into the dilution tunnel 16. The probe 30 collects a gas streamsample from the engine 12 and directs the gas stream sample to thedilution apparatus 22. The inlet of the probe 30 is preferablyiso-kinetic and positioned proximate the center of the dilution tunnel16 to minimize boundary effects caused by the walls of the tunnel 16. Inthe dilution apparatus 22, the sampled gas is diluted with dilution gas,cooled to ambient temperature, and thoroughly mixed with the dilutiongas.

The result is a full/partial/full dilution scheme, where the entireexhaust stream is initially diluted within the dilution tunnel 16, aportion of the exhaust stream is sampled by the sampling probe 30, andthe entire portion of the gas sample is then diluted in the dilutionapparatus. This full/partial/full dilution scheme is an improvement overconventional partial/full/partial dilution schemes, which direct only aportion of the exhaust stream into the dilution tunnel 16. As a result,the number of particles seen in resulting samples is low compared to afull/partial/full dilution scheme.

The gas mixture is then fed to the residence time chamber 24 which isdesigned to provide sufficient time for gas-to-particle conversion,which involves the diffusion limited transport of supersaturated vaporonto existing particles. The gas flow also becomes uniformly distributedbefore entering the sampling probes 26 a, b, . . . n. The samplingprobes 26 a, b, . . . n simultaneously collect multiple samples of thegas mixture and feed the samples to the sampling trains 28 a, b, . . . nwhich are constructed to take various samples of the gas. Preferably,the sampling trains are configured to sample unregulated chemicalspecies within the gas samples, for example volatile and semi-volatileorganics, gas-phase compounds, and particulate matter.

The components of the system 10 are preferably made of inert materials,including, but not limited to, stainless steel, plastic or polymermaterials such as TEFLON, and plastic or polymer coated aluminum such asTEFLON-coated aluminum. In addition, the use of electricallynon-chargeable materials, such as 304, 316 and 316L stainless steels,can also be used to reduce electrostatic deposition of charged particlesthat are typically polarized during combustion processes. In addition,the system 10 is preferably devoid of materials, for example oils,greases, rubbers and the like, that could outgas organics to avoidcontamination of the gas stream and gas samples.

Further, the system 10 is preferably configured to minimize vapor andparticulate losses. For example, the system is designed to promotesmooth flow transitions within the system 10.

Dilution Apparatus

With reference to FIGS. 1-4, the dilution apparatus 22 is designed to bethermophoretic-resistant to reduce the thermophoretic force on emissionparticles, thereby reducing particulate matter losses. In addition, thedilution apparatus 22 preferably simulates atmospheric dilution, mixingand cooling processes, enabling the sampled gas and the dilution gas tothoroughly mix and cool to ambient temperature, allowing gas-phaseorganics in the sampled gas to nucleate and condense to their usualaerosol phase.

The sampled gas collected by the sampling probe 30 enters the dilutionapparatus 22 through an inlet 32. As shown in FIGS. 3-4, the dilutionapparatus 22 has a cylindrical housing 34 with a first end 36 thatincludes the inlet 32, a second end 38 and an interior space. An innercylindrical wall 40 is located concentrically with the housing 34, withthe cylindrical wall 40 having a first end 42 adjacent the first end 36of the housing and a second end 44 adjacent the second end 38 of thehousing. The cylindrical wall 40 divides the interior space into astatic pressure chamber 46 defined between the housing 34 and the wall40 and that extends generally from the first end 42 of the wall to thesecond end 44 of the wall 40, and a mixing chamber 48 that extendsgenerally from the first end of the wall to the second end of the wall.

The wall 40 has circumferentially and axially distributed perforations50 near the first end 42 thereof that place the static pressure chamber46 in communication with the mixing chamber 48. In addition, the housing34 has a plurality of evenly, circumferentially spaced inlet ports 52near the second end 44 thereof that open into the static pressurechamber 46 for introducing a dilution gas into the static pressurechamber 46. The inlets ports 52 communicate with a plenum 54 definedaround the circumference of the housing 34, and dilution gas is fed tothe plenum 54 from a dilution gas source 56. If desired, the dilutiongas source 56 can be a source of over-pressure, such as a compressor,and a regulator 57, such as a valve, can be used to regulate the flow ofdilution gas into the dilution apparatus. The gas source 57 and/orregulator 57 can be used to control the amount of dilution gas that isfed to the dilution apparatus, thereby changing the dilution ratio ofthe gas stream sample and the dilution gas.

In use, the sampled gas enters the mixing chamber 48 of the dilutionapparatus through the inlet 32 as shown by the arrows in FIG. 3. Inaddition, dilution gas is introduced into the static pressure chamber 46through the inlets ports 52. As the dilution gas flows toward the firstend 42 as shown by the arrows in FIG. 3, it exchanges heat with thesampled gas in the mixing chamber 48. In an alternative embodiment,insulation material can be provided on the wall 40 to keep the innerpart of the wall 40 the same temperature as the sample gas, therebylowering the effect of thermophoresis.

Once the dilution gas reaches the perforations 50, it flows radiallyinward into the mixing chamber 48 to mix with the sampled gas. FIG. 3illustrates the flow of dilution air into the mixing chamber 48. Theperforation holes 50 create jets of dilution air that impinge upon thesampled gas to create turbulent mixing with the sampled gas. Preferably,the perforation holes 50 are configured to generally evenly distributethe dilution gas into the mixing chamber. In the illustrated embodiment,the holes 50 are circumferentially and axially evenly spaced about thewall 40. Mixing of the dilution gas and the sampled gas also cools thesampled gas.

The dilution gas is at a temperature lower than the sampled gas, so thatthe sampled gas is cooled through heat exchange with the static pressurechamber and as a result of mixing with the dilution gas, allowinggas-phase organics in the sampled gas to nucleate and condense to theirusual aerosol phase in the atmosphere. Preferably, the sampled gas iscooled to a temperature that is at least within 5° C. of ambienttemperature by the time the mixture of sampled gas and dilution gasreaches the exit of the dilution apparatus. More preferably, the sampledgas is cooled to ambient temperature by the time the mixture of sampledgas and dilution gas reaches the exit of the dilution apparatus. Incertain embodiments, the sampled gas can be cooled to a temperaturebelow ambient temperature.

In addition, because the sampled gas is cooled to at or near ambienttemperature, temperature differences between the exterior of theapparatus 22 and the gas mixture within the mixing chamber 48 isreduced, thereby reducing the thermophoretic force acting on particlesin the flow. This reduces particle loss as the gas sample flows throughthe dilution apparatus 22.

The number and size of the perforation holes 50 is chosen based on thegas being sampled, the gas temperature, and the desired dilution rate.For diesel engine exhaust, the holes can provide between 20% to 80%porosity, have diameters ranging from about 0.125 inch to about 0.5inch, and extend over a length L_(w) of the wall 40 ranging from about0.06 inches to about 15 inches (FIG. 3). In addition, the dimensions ofthe dilution apparatus 22 are chosen based on the temperature of thesampled gas and the flow rate. With reference to FIG. 3, for dieselengine exhaust, the length L_(c) of the mixing chamber 48 can varybetween 18.0 inches to 63.0 inches, the housing can have a diameter Dbetween 3.0 inches and 10.5 inches, and the gap G defining the staticpressure chamber between the wall 40 and the housing 34 can vary between0.2 inches and 2.0 inches.

As shown in FIG. 3, a reducing cone 58 is connected to the end of thehousing 34 and defines an exit 60 for the mixture of sampled gas anddilution gas from the dilution apparatus 22. The reducing cone 58includes a first constant diameter section 62 that connects to thehousing 34, a tapered section 64 that reduces in diameter to reduce thediameter of the flow path, and a second constant diameter section 66that defines the exit 60 and which is directly connected to theresidence time chamber 24. The reducing cone 58 helps to provide asmooth flow transition of the gas mixture from the dilution apparatus 22to the residence time chamber 24.

Further details on the dilution apparatus 22 can be found in copendingU.S. patent application Ser. No. 11/530,758, filed on Sep. 11, 2006, andtitled Thermophoretic-Resistant Gas Dilution Apparatus For Use inEmissions Analysis, which application is incorporated herein byreference.

Residence Time Chamber

The residence time chamber 24 is best illustrated in FIGS. 1, 2, 5 and6. The chamber 24 includes a housing 70 having a first end 72 and asecond end 74. In the illustrated embodiment, the housing 70 is orientedgenerally vertically so that the longitudinal axis of the housing 70 isoriented vertically and generally perpendicular to the longitudinal axisof the dilution apparatus 22 which is disposed generally horizontally.

The housing 70 is connected to the reducing cone 58 of the dilutionapparatus 22 at the first end 72. Preferably, the first end 72 is in theform of a conical section, with the cone opening or facing downward. Thegas mixture is received into the conical section 72, with the conicalsection helping to promote a smooth flow transition of the gas mixturefrom the dilution apparatus to the residence time chamber. Likewise, thesecond end 74 is in the form of a conical section, with the cone openingor facing upward. The conical section 74 helps to promote a smooth flowtransition from the residence time chamber to an exit port 76 located atthe bottom of the conical section 74.

The housing 70, except for the conical sections 72, 74, is generallycylindrical and has a constant diameter from the conical section 72 tothe conical section 74. The housing 70 provides sufficient time forgas-to-particle conversion within the gas mixture, and allows the gasflow to become uniformly distributed. Preferably, the housing 70provides at least 30 seconds of residence time for the gas flow from thetime the gas flow enters the housing 70 to the time the gas flow reachesand enters one of the sampling probes. A residence time of 30 secondscan be provided by a housing 70 with a height of about 57 inches and adiameter of about 12.0 inches.

As shown in FIGS. 5 and 6, the sampling probes 26 a, b, . . . n aredisposed inside of the housing 70 to simultaneously collect multiplesamples of the gas mixture and feed each sample to the sampling train 28a, b, . . . n. The sampling probes are aligned coaxial to the flowdirection to achieve isoaxial and isokinetic sampling. In theillustrated embodiment, 8 sampling probes are provided, with each of thesampling probes 26 a, b, . . . n extending upward with the inlets to theprobes facing upward toward the oncoming flow. To avoid boundary floweffects of the housing wall, the sampling probes are preferably spacedinwardly from the housing wall. Because the sampling probes are isoaxialand face upward toward the oncoming flow, sampling is improved becausethe sampled flow does not need to turn sharp corners to enter theprobes.

Further details on the residence time chamber and the sampling probescan be found in copending U.S. patent application Ser. No. 11/530,746,filed on Sep. 11, 2006, and titled Residence Time Chamber and SamplingApparatus, which application is incorporated herein by reference.

Sampling Trains

The gas samples entering the sampling probes 26 a, b, . . . n aredirected to the sampling trains 28 a, b, . . . n. The sampling trainscan be configured to take samples of any kind of matter within the gassamples. Preferably, the sampling trains are configured to sampleunregulated chemical species within the gas samples, for examplevolatile and semi-volatile organics, gas-phase compounds, andparticulate matter.

Examples of suitable sampling trains are illustrated in FIGS. 7 and 8.As shown in FIG. 7, sampling trains 28 a, 28 b, 28 c each begin with aPM2.5 cyclone separator 80 that can be operated at a flow rate of 16.7liters/min (lpm) for removing particles that are about 2.5 microns andabove. Flow through the trains 28 a, 28 b, 28 c is controlled bydownstream critical flow orifices 82 in series with a rotary vacuum pump84 via a manifold 86. A rotameter prior to each critical flow orificecan be used to monitor the flow rate. A filter 88, for example a twostage TEFLON membrane filter, is disposed after the separator 80 tofilter out material from the sampled gas. The filters 88 can then beanalyzed for collected material. When the filters 88 are TEFLON membranefilters, analysis can be conducted for total mass, particulate mattersulfate ions, and particulate matter trace elemental composition.

The sampling trains 28 d, 28 e, 28 f illustrated in FIG. 7 are similarto the sampling trains 28 a, 28 b, 28 c. However, the illustrated trains28 d, 28 e, 28 f utilize a filter 90, preferably a two stage quartzfiber filter, in series with a polyurethane foam (PUF) cartridge 92. Anadsorption material substrate, such as an XAD™ substrate, could be usedin place of the PUF cartridge in the case of higher flow rates. When thefilters 90 are quartz filters, particle-phase organic compounds can becollected to analyze for particulate matter organics, nitro-PAHparticulate matter, and particulate matter hydrocarbon distribution. Inthe case of PUF cartridges, semi-volatile organic compounds can becollected to analyze for semi-volatile organic compounds, semi-volatilenitro-PAH, and semivolatile hydrocarbon distribution.

With reference to FIG. 8, a sampling train 28 g that is designed forhigh flow samples is illustrated. The sampling train 28 g is connectedto the exit port 76 at the bottom of the conical section 74. Thesampling train 28 g is not connected to a sampling probe. Instead, thesampling train samples the remainder of the gas flow that is not sampledby the sampling probes as the gas flow remainder exits through thebottom of the residence time chamber 24. The train 28 g includes a PM2.5cyclone separator 100 that can be operated at a flow rate of 92liters/min (lpm) for removing particles that are about 2.5 microns andabove, followed in series by a filter 102, for example a quartz filter,a PUF cartridge 104 (or XAD substrate), critical flow orifices 156, anda rotary vacuum pump 106. This kind of sampling train 28 g is suitablefor use in collecting samples for polycyclic aromatic hydrocarbonanalysis from low emission sources. The sampling train 28 g can alsoinclude a flow meter 154, shown in FIGS. 1 and 2.

FIG. 8 also illustrates a gaseous sampling train 28 h which can be runin parallel to the sampling trains 28 a-f. The sampling train 28 hincludes two Dinitrophenyl-Hydrazine (DNPH) cartridges 110 arranged inparallel to collect samples which are subsequently analyzed for carbonylspecies. The cartridges 110 can have different flow rates, for exampleabout 1.5 lpm and about 0.3 lpm. The flow rates can be controlled bycritical flow orifices 112 in series with the rotary vacuum pump 106. Inaddition, the train 28 h can include two volatile organic compound (VOC)tubes 114 arranged parallel to the DNPH cartridges to collect samplesfor hydrocarbon speciation. The flow rates through the VOC tubes 114 canrange from about 10 standard cubic centimeter (SCCM) to 50 SCCM,controlled by two separate mass flow controllers 116 in series with thevacuum pump 106. The mass flow controllers 116 can also be used tocollect mass flow, volumetric flow, pressure, and temperature data. Ifdesired, one or two filters prior to the DNPH cartridges 110 and VOCtubes 114 can be used to collect large particles.

An additional sampling train 28 i can be used to measure particle sizedistributions for steady-state and transient operations. In addition, asampling train 28 j can include temperature, humidity, and pressuresensors to monitor the residence time chamber conditions.

Other types of sampling trains for collecting other types of materialswithin the sampled gas can be used. The sampling trains described hereinare intended to be exemplary and not intended to be limiting.

Further details on the sampling trains can be found in U.S. patentapplication Ser. No. 11/530,746, filed on Sep. 11, 2006, and titledResidence Time Chamber and Sampling Apparatus.

The method of operation of the system 10 and of sampling exhaust gasfrom the engine 12 is apparent from the preceding description. Withreference to FIG. 9, a sample of the exhaust gas from the engine isinitially directed into the dilution apparatus 22, through the samplingprobe 30. Next, in the dilution apparatus, the gas sample is cooled bythe dilution gas and the dilution gas and the gas sample are mixed. Thegas mixture is then directed to the residence time chamber, and asample, preferably a plurality of simultaneous samples, of the gasmixture is taken from the residence time chamber through a samplingprobe having an inlet substantially parallel to a direction of flow ofthe gas mixture within the residence time chamber. The sample is thendirected to a sampling train which is configured to remove a desiredmaterial from the sample for subsequent analysis.

The invention may be embodied in other forms without departing from thespirit or novel characteristics thereof. The embodiments disclosed inthis application are to be considered in all respects as illustrativeand not limitative. The scope of the invention is indicated by theappended claims rather than by the foregoing description; and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

1. A system for sampling emission products from an emissions source,comprising: a dilution apparatus connected to a sampling probe toreceive a gas stream sample, the dilution apparatus including anisokinetic inlet through which the gas stream sample enters, a dilutiongas inlet through which dilution gas enters the dilution apparatus, andan exit through which a mixture of dilution gas and the gas streamsample exits the dilution apparatus; a dilution gas source connected tothe dilution gas inlet of the dilution apparatus; a residence timechamber connected to the dilution apparatus and receiving therefrom thegas mixture, the residence time chamber including a plurality ofisoaxial sampling probes disposed inside the chamber; and a samplingtrain connected to each of the isoaxial sampling probes.
 2. The systemof claim 1, at least one of said sampling trains includes simultaneousparticulate matter sampling and gas sampling.
 3. The system of claim 1,wherein the residence time chamber is configured to provide at least 30seconds of residence time for the gas mixture prior to reaching thesampling probes.
 4. The system of claim 1, wherein the sampling trainsinclude a particulate matter sampling train, a gas sampling train, and avolatile and semi-volatile matter sampling train.
 5. The system of claim1, wherein the dilution apparatus and the residence time chamber areeach made of an inert material.
 6. The system of claim 1, wherein thedilution apparatus includes a conical section defining the exit; and theresidence time chamber includes a first conical section connected to theconical section of the dilution apparatus into which the gas mixture isreceived, and a second conical section at an exit of the residence timechamber.